This invention relates to a spreading code generator for generating a spreading code.
A spreading code is used in spread-spectrum communication for transmitting an information signal upon spreading the signal over a wide band of frequencies.
In CDMA (Code Division Multiple Access) communication which makes use of different spreading codes, it is possible to acquire multiple communication channels within a common frequency band. As a result, more efficient utilization of frequency can be achieved in comparison with conventional narrow-band communication.
In CDMA communication of this kind, users are identified within the common frequency band owing to the dissimilarity in the spreading codes used. For this reason, so-called orthogonality between spreading codes is necessary in order to prevent interference between users.
In such CDMA communication, transmission rate (transmission speed) can be changed by changing the code length of the spreading code sequence used. However, in a case where multiple users communicate using different transmission rates within the same frequency band, it is required to use spreading codes that are mutually orthogonal even though their periods differ.
In light of the above, a method of performing communication by spreading code sequences having a tree-like hierarchical structure has already been proposed as a CDMA communication scheme having orthogonality between spreading codes. [See Japanese Patent Application Laid-Open No. 10-290211 (which corresponds to EP Disclosure 814581).]
As shown in FIG. 9 illustrative of the prior art mentioned above, matrices Cn(m) (where n represents the order of the matrix and m the row number within the matrix) have a tree-like hierarchical structure. Matrices having the same matrix order n, e.g., matrices C2(1) and C2(2) and matrices C4(1) to C4(4), are in the same hierarchical layer and the spreading code sequences of the matrices in the identical layers are mutually orthogonal.
On the other hand, among the group of matrices Cn(m) connected in tree-like fashion in the vertical direction, matrices in which the row numbers are odd, e.g., matrices C2(1), C4(1), C8(1) . . . , have code sequences comprising two periods of the higher order component of these matrices. Matrices in which the row numbers are even, e.g., matrices C2(2), C4(2), C8(2) . . . , have code sequences comprising one period of the higher order component of these matrices and an inverted component obtained by inverting the higher order component.
Because the spreading code sequence of a lower order matrix is completely contained within the code sequence of a higher order matrix, the higher and lower order matrices connected in the tree structure do not possess orthogonality even though the code lengths differ. However, even though the code lengths are different, there is orthogonality between matrices not connected in the form of a tree.
For example, matrix C2(1) and matrix C4(1) or C4(2), with are tree-connected, do not possess orthogonality. On the other hand, matrices C2(1), C4(3) and C4(4), which are not tree-connected, do possess orthogonality though the code lengths differ.
As a result, in a case where multiple codes are selected at the time of multiple-rate transmission, assigning codes sequentially upon taking into consideration the relationship between the row numbers m of the matrices makes it possible to perform data communication using mutually orthogonal spreading codes whose periods differ.
In accordance with the prior art described above, a signal is obtained through spread-spectrum modulation of 2n (n greater than R) channels using a group modulator obtained by hierarchically connecting R stages of basic modulation elements comprising a multiplying element and an adding element.
However, with the above-described spreading code generator, connecting basic modulation elements hierarchically into R stages makes it impossible to avoid an increase in the scale of the circuitry because even the spreading code sequence of maximum code length is accommodated. This invites an increase in the size of the apparatus.
An object of the present invention is to solve the aforementioned problem.
Another object of the present invention is to reduce the size of the apparatus by simplifying the circuit structure that generates the spreading codes.
A spreading code generator according to the present invention, comprising:
storage means for storing a code; and
extending means for repeating inverted extension or non-inverted extension, depending upon a reference coefficient, of the code that has been stored in said storage means.
A spreading code generator according to the present invention comprising:
first storage means for storing a first code;
second storage means for storing a second code; and
extending means for repeating inverted extension or non-inverted extension, depending upon a reference coefficient, of the first and second codes stored in said first and second storage means.
A spreading code generating method according to the present invention comprising steps of:
an analyzing step of analyzing a reference coefficient; and
a repeating step of repeating inverted extension or non-inverted extension of a code depending upon the reference coefficient.
A transmitting apparatus according to the present invention comprising:
storage means for storing a code;
extending means for repeating inverted extension or non-inverted extension, depending upon a reference coefficient, of the code stored in said storage means; and
spreading means for spreading transmission data by the extended code from said extending means.
A transmission apparatus according to the present invention comprising:
first storage means for storing a first code;
second storage means for storing a second code;
a extending means for repeating inverted extension or non-inverted extension, depending upon a reference coefficient, of the first code and second code stored in said first and second storage means; and
spreading means for spreading transmission data by an extended code from said extending means.